Automatic stop circuit for motion picture projector

ABSTRACT

A sound motion picture projector which includes a control circuit responsive to the presence of an audio signal having a predetermined frequency on the sound track of the film being projected to interrupt the film drive means, whereby a particular frame of the film may be automatically projected as a still picture.

United States Patent Hutner [54] AUTOMATIC STOP CIRCUIT FOR MOTIONPICTURE PROJECTOR [72] Inventor: Mark A.IIutner,Gl enview, lll. 73]Assignee: Elco Corporation, Jenkintown, Pa.

[22] Filed: July 29, 1970 [21] Appl. No.: 59,226

[52] U.S. Cl. ..352/92, 352/17, 352/169,

, 352/180, 352/236 [51] Int. Cl. ..G03b 21/48 [58] Field of Search..352/92, 180, 236, 169, 17

[56] References Cited UNITED STATES PATENTS 3,353,688 l0/l970 Paintop..352/169 X [451 Dec.5,1972

2,892,900 6/] 959 Guttwein ..352/17 X 3,432,228 3/1969 l-lellmund......352/169 1,944,024 1/1934 Foster ..352/92 3,447,864 6/1969 Shadley..352/17 3,520,596 7/1970 ODonnell et al. ..352/92 PrimaryExaminer-Louis R. Prince Assistant Examiner-Frederick Shoon Attorney-D.R. Pressman [57] ABSTRACT A sound motion picture projector whichincludes a control circuit responsive to the presence of an audio signalhaving a predetermined frequency on the sound track of the film beingprojected to interrupt the film drive means, whereby a particular frameof the film may be automatically projected as a still picture.

6 Claims, 2 Drawing Figures SWITCH 40 T46? MSM! 85 ION PATENTEBuzn 51912 SHEET 2 BF 2 Jo mm mw AUTOMATIC STOP CIRCUIT FOR MOTION PICTUREPROJECTOR BACKGROUND OF THE, INVENTION It .is known in the prior artto'provide means for 1 stopping a motion picture projector so as todisplay for a period of time a particular frame on the film. This hasbeen done by providing some sort of slot, opening or cut-out on the filmadjacent the frame which it is desired to display as a still picture anda mechanical means to engage in the slot, cut-out or opening and by sodoing disenable the film drive mechanism. This approach necessitates amore or less permanent alteration of the film and may effect its qualityor life. Also, once the film is altered, it is relatively difficult tochange the location of the desired stop point or to add a new one. Inaddition, the cost of producing the film is increased.

Therefore, it is an object of this invention to provide a novel meansfor stopping a motion picture projector in order to project a particularframe as a still picture which does not necessitateanyphysicalalteration of It is another object of this invention toprovide a ture projector to display a particular frame as a stillpicture which utilizes control means which are solid state electrical. I

. It is a still further object of this invention to provide a novelmeansfor automatically stopping a motion picture projector to display aparticular frame as a still picture which includes a means whereby theparticular frame chosen may be changed or additional frames addedwithout physical alteration of the film.

SUMMARY OF THE INVENTION The foregoing and other objects of thisinvention are achieved in one embodiment by-providing a control circuitresponsive to a selected audio signal recorded on the sound track of afilm being projected which control circuit is effective to stop the filmdrive mechanism so as to permit the display of a selected frame as astill picture.

The invention itself is defined in the claims appended hereto andforming a part of this specification, while an understanding of thestructure and mode'of operation of an embodiment thereof may be derivedfrom the detailed description taken in conjunction with the drawingswhich: FIG.'1 is a schematic illustration of a sound motion pictureprojector embodying the invention; and

FIG. 2 is a schematic illustration of a control circuit in accordancewith the invention.

DETAILED DESCRIPTION FIG. 1 illustrates a sound rnotion pictureprojector embodying the invention. The particular projector illustratedin this figure in schematic fashion is one in which the film is storedin a cartridge of the type where the two ends of the film are securedtogether so as to form an endless film which may be-rerun continuously.A projector of this type is shown. in U.S. Pat. No. 3,514,195, issued onMay 26, 1970to O. R. Nemeth. It is to be understood, however, that otherand different types of projectors, including the more conventional 0ones having storage reels and take up reels, may be used.

The projector of FIG. 1 includes a housing. 2. A cartridge 4 containingan'endless film is provided and may be inserted in an opening in theside of the housing to engage with film drive, projection and sound pickup means in the manner to be described. The endless film is containedwithin the cartridge in a roll 6. A driven hub 8 engages the innermostconvolution of the film and pushes it through a guide channel 10. Fromthe exit end of the guide channel indicated at 12 the film passes to aguide 14 and past a projection aperture 16.

Below the projection aperture 16 the film passes over a guide 18 andfrom there around a movable element 20 which maintains a compensatingloop in the film. The film leaves the compensating loop and passesaround another guide 22 and is held against a feed sprocket 24 by meansof a pair of guides 26 and 28. After passing around the guide 28,another guide channel 30 is provided. The film exiting from the guidechannel 30 reenters the roll 6 so as to be recycled as desired.

The cartridge 4, in addition to including the projection aperture 16also includes an aperture 32 through which an audio signal pickup head34 has access to the film. Likewise, an opening 35 is provided in thecartridge for the feed sprocket 24.

The film drive means also includes an intermittent pawl 36 which feedsthe film intermittently pass the projection aperture 16 at the same rateat which the feed sprocket is rotating. The various feed elements, thatis the hub 8, feed sprocket 24 and intermittent pawl 36 are connected bya drive means represented by the dotted line connection 38 and areactuated by the output of a transmission means 40, the input of which isconstituted'by'a motor 492.

Another opening 44 in the cartridge accommodates a projection lamp 46mounted in the housing so that light from the lamp after passing throughthe'film is projected by the projection objective 48 onto the surface ofa reflector 50. Not shown in this drawing but positioned in the sameplane as the reflector 50 is another reflector which projects the imagebeam to the left as shown in the drawing so as to cause it to reach aviewing screen 52 mounted in one end of the housing. As noted above, theparticular projector illustrated is that shown in U.S. Pat. No.3,514,195 and reference may be had to that patent for a more detaileddescription of the projector including its projection system,

-. film drive means and the cartridge.

In accordance with the invention, the projector includes means for stpping the projector when it is desired to display a particular frame asa still picture The apparatus includes a solenoid 54 mounted in thehousing and actuating, through a mechanical linkage 56, the transmission40 so as to disenable the film drive when it is desired to stop the filmadvance. The particular film drive interrupting means may take a numberof forms. For instance, the transmission 40 could be constituted by acombination brake and clutch means operable when the solenoid 54 isenergized to disengage the clutch so as to interrupt the drive from themotor 42 and at the same time apply a brake so as to bringthe film to astop at the desired point. A specific mechanism for insuring that thefilm is brought to a halt at a desired point to insure that theparticular frame is accurately framed in the projector and toinsure thata shutter forming part of the projector is maintained in an openposition, but which forms no part of this invention, is shown in U.S.Pat. No. 3,647,288 to George J. Zahradnik and Arthur A. Pudark issuedMar. 7, 1972 for Automatic Mechanism For A Motion Picture Projectorandassigned to the same assignee as is this application.

In addition to operating the transmission system 40 so as to stop thefilm at the desired point, the linkage 56, actuated when the solenoid 54is energized, is also effective to operate a switch 58 for a purpose tobe hereinafter described. In addition, it is desired that when the filmis stopped to display a particular frame as a still picture it isdesirable to dim the projection lamp 46 and switch means operated by thesolenoid 54 may be provided for this purpose.

FIG. 2 of the drawing illustrates an embodiment of a control circuit inaccordance with the invention. The circuit includes an audio signalpreamplifier 60 receiving as an input the signal detected by the audiopick up head 34. This signal is received via an input terminal 62 andafter amplification is supplied as an output via a conductor 64 to anaudio poweramplifier 66. The output of the audio power amplifier appearson the output conductors 68 and 70 and is supplied to the operating coil72 of a speaker. Included in the audio output circult is the movableterminal 74 of the switch 58 which in its normal unactuated positionconnects the speaker to the audio power amplifier 68. a

The output of the preamplifier is also supplied via a conductor 76 tothe input of the control circuit 78 forming a part of the invention.Inasmuch as the preamplifier, audio power amplifier and control circuitare constituted by solid state electronic components, direct currentoperating voltage for these elements may be supplied from a conventionalrectifying power supply driving its input alternating current from atransformer in the projector (not shown). It is contemplated that theaudio signal may be derived from magnetic tape constituting a soundtrack on film so that the pick up head 34 is a device responsive tovariations in the signal recorded on such tape.

In order that the film may be stopped at a desired point, a prerecordedtone is placed on the film sound track. This tone may be superimposed onthe audio program material and in one embodiment it has been founddesirable to use an 80 Hz signal which is 350 miliseconds in duration.The particular signal suggested was selected in a system where the audiosystem including the tape, pick up head and amplifiers had a goodresponse in the middle audio range and a low frequency signal such asone of 80 Hz is one which would not be heard by the listener.

Thus, the output of the preamplifier 60 is applied across apotentiometer 80 which acts as a sensitivity control. The audio signalis then coupled by a capacitor 82 to a narrow band-pass amplifier 84including an NPN transistor 86 and a filter circuit 88 which isconstituted by a combination of resistive and capacitive elementsconnected in the manner well known in the art so as to pass only signalsof a desired frequency. As indicated, the frequency selected in oneembodiment was 80'l-lz so that the output of the band-pass amplifier 84appearing on the collector of the transistor 86 is only signals of thatfrequency amplified. That output is coupled via a capacitor 90 to thebase of a PNP transistor 92 having its emitter connected to the positivebus 94 while its collector was connected to the negative bus 96 througha resistor 98. Connected between the positive bus 94 and the base of thetransistor 92 is a biasing resistor 100. The value of the biasingresistor is selected so as to permit conduction of the transistor 92only in response to negative going signals exceeding a predeterminedvalue. By this means an operating voltage level is established to insurethat there is no response to other 80 Hz signals which do exceed thislevel and thus the possibility of undesired stops is lessened.

The collector of the transistor 92 is directly coupled to the base of atransistor 102. The transistor 102 has its collector coupled through acapacitor 104 to the positive bus 94 while its emitter is connected tothe collector of a transistor 106, the emitter of which is connected tothe negative bus 96. A time delay circuit is provided by a resistor 108connected to the positive bus 94 and to a capacitor 110. The time delaycircuit also includes a zener diode 112 having its anode connected toone end of a resistor 114 the other end of which is connected to thenegative bus 96. The base of the transistor 106 is connected to thejunction of the zener diode and resistor 114 so that its conduction iscontrolled by current passed by the zener diode when it conducts. As maybe seen, the transistor 106 is arranged to control the conduction of thetransistor 102 depending on whether itv itself is conducting ornonconducting.

The collector of the transistor 102 is connected to one end of aresistor 116 the other end of which is connected through a resistor 118through the positive bus 94 and to the base of a PNP transistor 120. Theemitter of the transistor 120 is connected through a transistor 122 tothe base'of a transistor 124 and through a resistor 126 to the negativebus 96. Connected in series with the collector of the transistor 12 4and the positive bus 94 is the operating coil 126 of the solenoid 54. Adiode 128 is poled with its cathode connected to the positive bus 124 inparallel with the operating coil 126 to act as a free wheeling diode.

The operation of the circuit is as follows. The audio input signal as anoutput of the preamplifier 60 is supplied as an input to the circuit 78and upon the receipt of an audio signal of the selected frequency thatsignal would be amplified by the band-pass amplifier 84 and supplied asan input to the base of the transistor 92. By virtue of the positivebias supplied to that transistor only the negative portions of thepreselected tone signal in excess of a predetermined value would befurther amplified and supplied as an input to the base of the transistor102. Assuming conduction of the transistor 106, the transistor 102 willthen conduct and amplify those signals which will appear in the form ofsuccessive pulses on its collector. Those pulses will be integrated bythe combined effect of the capacitor 104 and resistors 116 and 118; andsupplied as a continuous signal as an input to the base transistor 120causing it to conduct. The conduction of the transistor 120 in turncauses the transistor 124 to conduct energizing the solenoid operatingcoil 126. The energization of the solenoid coil 126 would then beeffective to cause movement of its connections 56 to the transmissionmeans ill so as to stop the movement of the film at the desired point.At the same time the transmission40 is operated by the solenoid 54, theswitch 58 is operated causing its contact 74 to open the connection tothe speaker coil 72 and complete a circuit via a conductor 128 through aresistor 130 connected to the junction of the capacitor 110 and zenerdiode 112.

When a sound motion picture projector is started up, there is a periodwhere the film and the magnetic sound track thereon is moving from'zerospeed to its operating speedyDuring this interval a signal on the .soundtrack thereof of higher frequency'm'ay appear lower because of'thereduced speed. For example, if 80 Hz is selected as the desiredfrequency a recorded signal of 160 Hz which is otherwise intended as. anaudio signal 7 may momentarily supplya 80 Hz input to the preamplitier.Were this signal to be effective to actuate the control 'circuitthesolenoid 126 would be energized and stop the movement of the film eventhough it was not intended. To eliminate this problem the time delaycircuit is provided. Thusywhen the projector has stopped, the capacitor110 is held at ground. At start up this capacitor charges from thepositive bus 94 through the resistor W8. A time delay is thereforeprovided while the capacitor 110 is charging to a value sufficient tocause zener 112 to conductthereby supplying a positive going signal atthe base of the transistor N96 whereby it may conduct. By virtue of thistime delay an interval is provided during which the film can accelerateto its normal operating speed. Thus, spurious tone signals will not beeffective to energize the solenoid 126 as the transistor 102 cannotconduct until the transistor 106 has an appropriate positivesignal'supplied .to its base. it should be noted that this time delayalso provides another benefit. It prevents transients which may occurwhen power is applied from operating the solenoid as such transientswould not be effective during the charging interval of the capacitor 110and the consequent non-conduction of transistor 106.

As pointed out above, when the solenoid is energized, the contacts ofswitch 58 disconnect the speaker coil from the output terminal 68 whichoutput terminal is the negative bus of that amplifier and connects thatterminal to the conductor 128. When this occurs, the capacitor i110which is now charged fully permitting the conduction of the transistor106 discharges to the negative bus through the resistor 13%. Theresistor 1310 is optional as it is of low value and is merely'desired toprotect the contacts of switch 58 from high current due to the dischargeof capacitor Kilt). When the capacitor has discharged to a predeterminedvalue, the transistor ltlti ceases conduction as does the transistor102causing the solenoid coil 126 to become deenergized. The timenecessary for the capacitor 110 to discharge is determined by theenergization period of the solenoid.

Generally, it is desired that it be energized only long enough tooperate a stopping mechanism such as that shown in the patent to GeorgeJ. Zahradnski and I Arthur A. Puda rk, referred to above. When theparticular frame has been projected a desired timed, the mechanism maybe operated to cause the-projector to operate as a motion picture asexplained in that application. When the solenoid is deenergized, theswitch terminal 74 again connects the speaker coil 72- to the outputterminal 63 interrupting the discharge circuit for the capacitor 110permittingit to charge up once again through the resistor 108 so thatthe control circuit is rendered effective to respond to the next timethe predetermined tone signal is detected.

In order that a manual stopping meansmay be provided, a pushbuttonswitch 132 is connected across the transistor 102. Upon the momentaryclosure of this switch, the transistor 102 is shunted and the transistor120 will then conduct causing the transistor 1.24 to con- I ductas'before energizing the coil 126; After the actuation of the solenoid,the projector will hold the desired frame until it is restarted asbefore. Thus, the apparatus provides both an automatic and manuallyoperated means whereby a selected frame can be displayed as a a LettersPatent of the United States is:

. film for stopping said film advance, said control means includingcircuit means for amplifying a discrete audio signal, means, connectedto said circuit means and operable in response to the amplified discreteaudio signal to disenable'said film advance means, said circuit meansincluding (1) a band-pass amplifier for amplifying only a selected rangeof frequencies recorded on said film track, and (2) means fordisenabling said circuit means for a predetermined time after saidprojector is started.

2. The projector of claim 11 wherein said means for disenabling saidfilm advance means includes means for interrupting and stopping saidtransmission means.

3. The apparatus of claim 2 wherein said circuit means includes asolenoid energizable in response to the detected presence of thediscrete audio signal on the track on said film and said means forinterrupting and stopping said transmission means is operativelyconnected to the armature of said solenoid.

4. The apparatus of claim 3 wherein said circuit means also includesmeans for amplifying unipolar portions of said discrete tone signal inexcess of a predetermined value; means for integrating the amplifiedunipolar portions; a solenoid operating coil; and amplifying meanscoupling the output of said integrating means to said solenoid operatingcoil to cause said coil to be energized in response to the presence ofan output from said integrating means.

5. The apparatus of claim 4 wherein said amplifying means coupling theoutput of said integrating means to said solenoid includes a firsttransistor having its input connected to the output of said means foramplifying unipolar portions of the discrete tone signal and its outputconnected to said integrating means; a second transistor connected inseries with said first transistor, whereby the ability of said firsttransistor to conduct is controlled in response to the conductive stateof said second transistor; a time delay circuit connected to theresistor; and a zener diode connected to the junction of said capacitorand said resistor and to the input electrode of said second transistor,whereby said second transistor will be rendered conductive when saidcapacitor is charged to the zener voltage.

1. In a sound motion picture projector including: means for storing filmto be projected; means for projecting images from said film onto aviewing surface, means, including transmission means, for advancing saidfilm past a projection means, and means for detecting and amplifyingaudio signals recorded on a track on said film; the improvementcomprising: control means responsive to a discrete audio signal recordedon said film for stopping said film advance, said control meansincluding circuit means for amplifying a discrete audio signal, meansconnected to said circuit means and operable in response to theamplified discrete audIo signal to disenable said film advance means,said circuit means including (1) a band-pass amplifier for amplifyingonly a selected range of frequencies recorded on said film track, and(2) means for disenabling said circuit means for a predetermined timeafter said projector is started.
 2. The projector of claim 1 whereinsaid means for disenabling said film advance means includes means forinterrupting and stopping said transmission means.
 3. The apparatus ofclaim 2 wherein said circuit means includes a solenoid energizable inresponse to the detected presence of the discrete audio signal on thetrack on said film and said means for interrupting and stopping saidtransmission means is operatively connected to the armature of saidsolenoid.
 4. The apparatus of claim 3 wherein said circuit means alsoincludes means for amplifying unipolar portions of said discrete tonesignal in excess of a predetermined value; means for integrating theamplified unipolar portions; a solenoid operating coil; and amplifyingmeans coupling the output of said integrating means to said solenoidoperating coil to cause said coil to be energized in response to thepresence of an output from said integrating means.
 5. The apparatus ofclaim 4 wherein said amplifying means coupling the output of saidintegrating means to said solenoid includes a first transistor havingits input connected to the output of said means for amplifying unipolarportions of the discrete tone signal and its output connected to saidintegrating means; a second transistor connected in series with saidfirst transistor, whereby the ability of said first transistor toconduct is controlled in response to the conductive state of said secondtransistor; a time delay circuit connected to the input electrode ofsaid second transistor, whereby said second transistor is prevented fromconducting for a predetermined time after said projector is turned on.6. The apparatus of claim 5 wherein said time delay circuit includes aresistor and capacitor connected in series; means for charging saidcapacitor through said resistor; and a zener diode connected to thejunction of said capacitor and said resistor and to the input electrodeof said second transistor, whereby said second transistor will berendered conductive when said capacitor is charged to the zener voltage.